Burner control system



Feb. 6, 1945. F. E. LANGE 2,368,850

BURNER CONTROL SYSTEM Filed Dec. l5, '1941 ATTORNEY ...couple isemployed to generate current for a Patented Feb. 6, 1945 yomni!) STATESPATENT Afir-FICE.

BURNER CONTROL ASYSTEM Frederick E. Lange, Lincoln, Nebr., vasslgnox' toj Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., acorporation of Delaware Y Application December 13, 1941, Serial No.422,849

7 Claims'. (Cl. 15S-117.1)

The present invention relates to a burner contrcl system and moreparticularly to one employing a thermoelectric device for controllingthe ow of fuel to the burner, although the present invention could wellbe used with other types of temperature responsive mechanisms.

In uid fuel burner control systems, particu-l larly thcse concerned withgaseous fuels, it is customary to employ a pilot burner for igniting asecond burner, usually the main burner. It is the usual practice withsuch systems to employ some means for interrupting the flow of fuel tothe main burner when the pilot burner is extin.

guished. One common ferm of such a protective means employs atherniocouple responsive to the heat ofthe pilot flame and whichgenerates a controlling current only when the thermocouple is heated bythe pilot burner. These arrangements have the serious disadvantage thatthe power produced by the thermocouple is necessarily extremely limited.In order to maintain the resistance as low as possible, it is necessaryto use relatively short elements for the thermocouple. When this isdone, the cold junction is necessarily suiliciently close to the hotjunction that it is unduly influenced by the main burner. This reducesthe temperature dlerence between the het and cold junctions of thethermocouple. This limitation on the amount of power generated by thethermocouple becomes extremely serious, Where, as hasbeen proposed, thethermotemperature controlling system.

An object of the present invention is to provide a safety control systemfor a burner employing a pilot light, which safety control system willbe quick in its response and relatively unaffected by the presence orabsence of a main burner flame.

Another object of the present invention is to provide a burner control.system employing thermoelectric means for detecting the condition of apilot burner in which provision is made for increasing the output of thethermoelectric means in spite of the influence ofthe main burner.

A further object of the invention is to provide an' arrangement of thetype discussed in which the normally cold junction of the controllingthermocouple is located so as to be exposed to the main burnertemperature but in which an additional thermoccuple is provided which isoperative upon the main burner temperature increasing to supplement thecurrent supplied by the controlling thermocouple.,

A further object of the invention is to provide a burner control systeminvolving a pair of burners in which there is a pair of thermocouplesaiding each other, the hot junctions of .the two thermocouples beingexposed to the flames of the two burners respectively and in which thecold junction of the thermocouple normally affected by the rst of theburners is exposed to the heat produced by the vsecond of the burners.

Other objects of the invention will be apparent from a consideration ofthe accompanying specication', claims, and drawing, of which:

The single figure is a schematic illustration of a burner'controlinvolving my invention.

Referring to the drawing, 'a portion of a conventional gas furnace is'illustrated and is indicated by the reference numeral I0. This furnacein the usual manner comprises the furnace II and a casing or jacket I2surrounding the furnace. Disposedwithin the furnace is a main gas burnerI3, a pilot burner I4, and a bleed gas burner I5. The pilot burner I 4is employed to ignite the main burner I3 and the bleed gas burner. Themain burner- I3 has the usual spuds I1.

A pipe I8 supplies gas to the main burner and is connected by a valve I9with a, main gas supply pipe 20. Pipe 20 leads to any suitable source ofgas supply (not shown)l The pilot burner I4 at a point on the inlet sideof valve I9.

The valve I9 is illustratively shown as adiaphragm gas valve. While thedetails of this valve do not, by themselves, form part of the presentinvention, they are brieyvdescribed in order to understand more fullythe operation of the system. The valve comprisesY a valve casing 2|having the -usual partition Wall providing a valve seat with whichcooperates `a valve disk 22. The valve stem 23 secured to valve disk 22is connected to a diaphragm 24.` An upper casing member Y25 encloses theupper side of the.diaphragm 24 so as to form with the valve casing 2I,upper f pressure in the upper diaphragm chamber. 'I'he pressure in thischamber is controlled by a threeway pilot valve 21. This valve `is ofconventional structure and the details thereof have Abeen omittedinorder to simplify the drawing. Communicating with the valve chamber 21isa pipe 28 connected to the upper diaphragm chamber, a pipe 29connected to gas supply pipe'2, and a pipe 30 leading from pilot valve21 to the bleed burner I5. The valve 21 is electromagnetically operatedand the coil of the electromagnet has been schematically shown in thedrawing in order to illustrate more fully the electric connections ofthe system. In general, the pilot valve 21 is so arranged that when thecoil 32 is energized, the gas above the diaphragm passes out throughpipes 28 and 30 to the bleed burner I5 and further gas is prevented fromentering the chamber above the diaphragm. The result is that the gaspressure acting beneath the diaphragm raises the valve disk 22 andadmits gas to the main burner I3. When the coil 32 is deenergized, theflow of gas from pipe 28 to pipe 30 and hence to the bleed gas burner I5is interrupted and gas is again permitted to ow from supply pipe 20 topipe 28 and hence to the upper chamber above the diaphragm. This permitsthe supply gas pressure to be applied above the diaphragm to cause thevalve disk 22 to again engage its seat.

Thus, when coil 32 is energized, gas is admitted to the main burner I3and when it is deenergized, this gas flow to the main burner isinterrupted.

The energization of coil 32 is controlled in part by a room thermostat35. This room thermostat comprises a bimetallic element 36 'to which issecured a contact arm 31 adapted to be moved into engagement with thecontact 38. As indicated by the legend, the bimetallic element 36 is soarranged that upon a drop in temperature the con. tact arm 31 is movedto the left into engagement with contact member 38. Upon a rise intemperature, the contact arm 31 is moved to the right out of suchengagement.

The current .for energizing coil 32 is supplied by a pair ofthermopiles'4i) and 4I. As will be presently explained, thesethermopiles not only supply the current for the operation of the controlsystem but also supply this current in accordance with the presence orabsence of a fiame at the pilot burner and hence act to indicate whetheror not the pilot burner is ignited.

Referring specifically to thermopile 48 which may be considered to bethe main control thermopile, this thermopile comprises a plurality ofelements 44, 42l 48 and 43 connected alternately and in series with apluralitv of elements 46. 45, and 41, The elements 42, 43, 44,and 48 areformed of material having thermoelectric characteristics which aredifferentfrom those of which elements 45 to 41 are formed. In otherwords. these elements form a plurality of thermocouples connected inseries` with each other so as to form Junctions 50, 5I, and 52 on theone hand, and junctions 53, 54, and 55 on the other hand. The junctions50, 5I, and 52 may for convenience be referred to as the hot junctionsand the junctions 53, 54, and 55 as the cold junctions. The hotjunctions 50, 5I, and 52 are exposed to the flame of the pilot burner.These junctions may be exposed to the main ame of the pilot burner or toa runner fiame 51 as illustrated in the drawing, but in any event, thehot junctions should be influenced less by the main burner than the coldjunctions. The cold junctions 53, 54, and 55 are exposed to the flame ofthe main burner. It will be noted that these junctions are located asubstantial distance above the spuds I1 so as to be exposed to arelatively hot portion of the main burner. However, the junctions 53,54, and 55 are not located directly in the main burner flame and thethermopile 40 is preferably so located that these junctions are heatedto approximately the same extent by the main burner flame as junctions50, 5I, and 52 are heated by the pilot burner flame.

The thermopile 4I comprises a plurality of members 60, 6I and 62 and afurther plurality of members 63, 64, and 65. The members 60, 6I and 62are formed of the same material as members 45, 46, and 41 and themembers 63, 64, and 65 are of the same material as members 42,143, 44and 48. The members 6l) to 65 are connected together alternately inseries so as to form junctions 68, 69, and 10 'and junctions 12 and 13.The two extreme ends of members 60 and 65 together constitute a thirdjunction. The junctions 68, 69 and 10 may be termed the hot junctions ofther- 'mopile 4I "and the remaining junctions including junctions 12 and13, the cold junctions.

The two thermopiles 40 and 4I are connected in series with each other tothe coil 32 of control device 21 and under the control of thermostat 35.The circuit connecting these members together is as follows: throughmembers 60, 63, 6I, 64, 62, and 65 to conductor 16, to thermocouplemembers 43, 41, 48, 45, 42, 46 and 44, then to conductor 11, bimetallicelement 36, switch blade 31, contact 38, conductor 18, coil 32, andconductor 19 back to thermocouple member 66. It will be noted from theforegoing circuit and from a comparison of the manner in which thethermocouples are connected in the circuit that4 the thermopiles 40 and4I are connected in series so as to aid each other. In other words, theextreme right hand hot junction of the thermopile 4I is junction 10. Thenext junction will of necessity be a cold junction if the thermocouplesare Aconnected so as to aid each other. It will be noted that themembers 43 and 65 which are of the same material are connected togetherby wire 16 so as to be in eect one continuous member. Thus, the firstthermoelectrc junction proceeding to the right is junction 53 which is acold junction. The next succeeding junction is junction 52 which is ahot junction. Thus, when junctions 50, 5I and 52 are considered as hotjunctions, the thermopiles are connected so as to aid each other. Thejunctions 68, 69, and 10 are preferably located adjacent a slightlycooler portion of the main burner than the cold junctions 53, 54, vand|55. This is not absolutely essential but does oier certain advantages,as will be ex- Lplained later. The lower ends, including the coldjunctions, of thermopile 4I are located in as cool a position aspossible. The fact that the hot junctions 68 to 10 are located adjacenta portion of the burner ame which is not quite so hot. makes it possibleto place the cold junctions of the thermopile 4I in a, lower portion ofthe furnace than would otherwise be possible. Inasmuch as thetemperature within a furnace decreases very rapidly below the uppersurface of the main burner, it is possible to place junctions 12 and 13in a rather cool location. This tendency of the furnace temperature todecrease rapidly below the level of the main burner is due to the inflowof secondary air to support 'combustion. The temperature of thissecondary air is sufficiently close to furnace room temperature that theregion around cold junctions 12 and 13 tends to remain at all times at asubstantially constant and relatively low temperture.

Operation Let it rst be assumed that the thermostat 35 is satisfied, asshown in the drawing, and that the pilot burner is ignited. Under theseconditions, it is impossible'for current to flow to coll 32 regardlessof whether energy is generated by thermopiles 40 and 4I. Consequently,as previously explained, the control device 21 is in such a positionthat communication is established between pipes 29 and 28 so that gaspressure exists above diaphragm 24 and valve disk 22 is maintained inclosed position. Because of the valve disk 22 vbeing closed, no gasflows to the main burner and this burner is unignited.

Let it be assumed that the pilot burnerl I4 is properly ignited. Underthese conditions, the junctions 50, I, and 52 are heated by the pilotburner ame 51. Due to the fact thatl the main burner is not inoperation, junctions 53, 54, and

55 are relatively Acold and all of the junctions of the thermopile 4Iare cold. Consequently,the action of the thermopile 40 is that of asimple thermopile in which the hot junctions are heated and the coldjunctions are maintained at a relatively low temperature, whilethermopile 4I acts merely as a' conductor. Under these conditions, ifthe room thermostat 35 now calls for heat, current is able to ilow overthe circuit previously traced. The thermopile 4D is designed to operateunder these conditions to generate suflcient current to energize coil32' so as to cause the latter to change the position of the pilot valveof control device 21. When this happens, as previously explained, gasilow between pipes 29 and 28 is interrupted and communicationisestablisl1ed between pipes 28 and 30 to permit the gas above diaphragm24 to pass to the bleed burner I4. The result of this is that the gaspressure above diaphragm y24 is relieved and valve I9 is opened topermit gas to now to the main burner.

The gas flowing to main burner I3 is ignited by the pilot burner I4 inthe usual manner. As soon as it becomes ignited, the cold junctions 53to 55 begin to 'be heated. As these junctions become heated, theelectromotive force developed by thermopile 40 decreases. Eventually,the point is reached at which the hot and cold junctions of thermopile40 vassume substantially the same temperature. If it were not forthermopile 4I the coil 32 would be deenergized and the main valve shutdo-Wn. During,r this time, however, the hot junctions of thermopile 4Iare also being heated by the main burner although to a slightly lessextent. As previously pointed out, thermopiles 40 and 4I are connectedto aid. each other. Thus. as the electromotive force generated bythermopile 45 decreases, that generated by thermopile 4I increases.Because of the fact that the cold junctions of thermopile 4I are in arelatively cool location, the electromotive force generated by thisthermopile is-substantially equal to that normally generated by thethermopile 40 when the main burner is unignited. As a result, the totalpower supplied by the thermopiles 45 and 4I remains substantiallyconstant, even though junctions 68to 10 are not aiected to the samedegree by the main burner as junctions 53 to 55.

Let it now be assumed that the thermostat 35 becomes satisfied. Theenergizing circuit for coil 32 is now interrupted so that valve I9 isclosed. This interrupts the ilow of 'gas to the main burner, sc thatitis extinguished. The thermopiles 40 and 4I then cool down to theprevious condition described in which junctions 50, 5I. and 52 are theonly junctions that are heated.

The operation which has been described so far is the normal operation ofthe system. The various abnormal conditions for which the system isdesigned will now be described. The simplest abnormal condition is thatof the pilot burner being extinguished along with the main burner at thetime that the thermostat calls for heat. It is obvious that under theseconditions, both thermocouples 40 and 4I will be unheated throughout andthat there is no source of power for energization of the coil 32.Consequently, the valve I9 will not be opened. Thus a ow oi gas to themain burner is prevented because of the absence of any pilot ilame toignite it.

Let the case now be considered in which the main burner and the pilotburner have 'both been ignited and the pilot burner is'extinguishedwhile the main burner continues in operation. It is generally desirableunder these conditions to terminate the operation of the main burner asits operation in the absence of a pilot flame may result in hazardousconditions. As soon as the pilot burner goes out, the junctions 50 to5.2 are' no longer heated bythe pilot burner. The only heat that thesejunctions receive is the relatively small amount of heat they receivefrom the mainr vburner by convection, radiation, and conduction. In anyevent, the junctions 53, 54, and 55 which are heated to a relativelyhigh degree by the main burner will be at a much higher temperature thanjunctions 50 to 52. As a result, an electromotive for-ce is generatedwhich is o-pposite in polarity to that'generated by thermopile 4I.Moreover, even though the normally hot junctions (now the coldjunctions) are heated to a certain extent Iby the main burner, the totalelectromotive force generated `by thermocouple 4I) will be very close inmagnitude to that generated by thermopile 4I due to the, fact that thehot junctions 53 to 55 are adjacent a hotter part of themain 4burnerflame than junctions 68 to 10. As a result, the voltage generated bythermopile 4Uv will overcome the voltage generated bv thermopile 4I soas to cause deenergization of coil 32. Thus, the coil 32 will be veryquickly deenergized so as to cause closureof valve I9 upon the pilotburner being extinguished even though the main burner is in operation.

` It will be seen from the above that regardless of whether the mainburner is in operation or not, the extinguishment of the pilot burnerinsures prompt deenergization of the coil 32. Furthermore, the totalpower generated by thermopiles 40 to 4I can be considerably greater thanthat generated by a' thermopile whose hot junctions are al1 locatedadjacent the pilot flame and whose cool junctions are located in as coola location as possible'. Inevitably, in such a case, the cool junctionsare affected to a considerable extent by the main burner ame. This isnecessary, as previously explained, because of the fact that thethermocouples must be of .relatively short length and that in order tolocate the hot junctions adjacent the pilot burner name, it is necessaryto have the cold junctions at a point where the main burner will af forpurposes of illustration only and that the invention is to be limitedonly by the scope of the appended claims.

What I claim is:

1. In combination, rst and second sources of heat, an electricallyoperated control device, and a plurality of thermocouples eiectivelyconnected to said device in series with each other, the hot junction ofone thermocouple being exposed to the ilrst source of heat and the coldjunction to the second source of heat, and the hot junction of the otherthermocouple being exposed to the second source of heat and the coldjunction being located in a region having a relatively low temperaturein respect to either source of heat so that said thermocouples areeffective to energize said device when either the first source alone orboth sources of heat are active but are ineffective to energize saiddevice whenever said rst source of heat is inactive.

2. In a burner control system, a pair of burners, a first of saidburners serving to ignite the second burner, an electrically operateddevice for controlling the delivery of fuel to the second burner, and aplurality of thermoelectric devices connected to said electricallyoperated .device and controlling the energization of said device, one ofsaid thermoelectric devices being operative in accordance with thedierence between the temperatures adjacent the ame portions of saidiirst and second burners, and the other being operative 'in accordancewith the difference. between the temperature adjacent the ame portion ofthe second burner and a region of relatively constant temperature andhence suppleinenting the output of said rst named thermoelectric deviceas said output decreases dueto the operation of said second burner.

3. In a burner control system, a main burner-,

a pilot burner, an electrically operated device for controlling thesupply of fuel to said main burner, and a plurality of thermocouplesconnected to said device in series with each other, the hot junction ofone thermocouple being exposed to the heat of the pilot burner and thecold junction to the heat of the main burner, and the hot junction ofthe other thermocouple being exposed to the heat ofthe main burner andthe cold junction being located in a region having a relatively constanttemperature so that said thermocouples are effective to energize saidAdevice when either the pilot burner alone or both the main and pilotburners are ignited but are ineffective to energize said device wheneversaid pilot burner is extinguished.

4. In a burner control system, a main burner, a pilot burner, anelectrically operated device for controlling the supply of fuel to saidmain burner, and a pair of thermocouples connected to said device inseries with each other, the hot junction of one thermocouple beingexposed to the heat of the pilot burner and the cold junction of saidthermocouple to the heat of the main burner, and the hot junction of theother thermocouple being exposed to the heat of the main burner and thecold junction being located in a region having a, relatively constanttemperature,-

-said thermocouples being so positioned with respect to the main burnerthat the hot junction of said last named thermocouple is heated to alesser extent by said main burner than the cold junction of said firstnamed thermocouple, said thermocouples being effective to energize saiddevice when either the pilot burner alone or both the main and pilotburners are ignited but are ineffective to energize said device wheneversaid pilot burner is extinguished.

5. In a burner control system, a pair of burners, a rst of said burnersserving to ignite the second burner, an electrically operated device forcontrolling the delivery of fuel to said second burner, a,thermoelectric device controlling the energization of said electricallyoperated device, said thermoelectric device being operative inaccordance with the difference between the'temperatures adjacent twoportions thereof, one of which is closer to the rst burner lthan theother and the other of which is substantially affected by the heat ofsaid second burner, and means automatically operable upon' the secondburner being ignited so as to raise the temperature of thev otherportion of the thermoelectric device to apply to said electricallyoperated device an electromotive force of suiiicient magnitude tocompensate for the decrease in magnitude .of electromotive forcegenerated by said thermoelectric device.

6. In a burner control system, a pair of burners, a first of saidburners serving to ignite the second burner, an electrically operateddevice for controlling the delivery of fuel to said second burner, athermocouple controlling the energization of said electrically operateddevice and having its hot junction located closer to said iirst burnerthan its cold junction and its cold junction being heated appreciably bysaid second burner, and means automatically operable upon the secondburner being ignited so as to raise the temperature of the cold junctionof said thermocouple to apply to said electrically operated device anelectromotive force of suilicient magnitude to compensate for thedecrease in magnitude of electromotive force generated by saidthermocouple.

7. In a burner control system, in combination, a main burner, a pilotburner for ignting the main burner, a device in control of the flow offuel to the main burner, a, first temperature responsive means havingtwo portions adapted to be respectively heated by the main and pilotburners and arranged to provide a force the direction and extent vofwhich depends upon the relative temperatures of said two portions toprovide a substantially zero force when said portions are equallyheated, a. force in a rst direction when the portion exposed to thepilot burner is hotter than the other portion and a `force in a seconddirection when the portion exposed to the pilot burner is lesshot than`said other portion, a second temperature responsive Imeans subjected tomain burner heat arranged to `provide a substantially zero force whensaid main burner is extinguished and to provide a force in said iirstdirection when said main burner is lighted, and means associating saidtemperature responsive means and said device whereby substantially noforce is provided for said device when both burners are extinguished, aforce in said rst direction is provided for said device by said secondtemperature responsive. means whenv both burners are ignited, a'force insaid first direction is provided for said device by said firsttemperature responsive means when the pilot burner only is lighted, andsubstantially no force for said device is provided as a result of theinteraction of said forces in said rst and second directions when themain burner is lighted and the pilot burner is extinguished.

FREDERICK E. LANGE`

